1. Technical Field
The present invention relates to a mechanism for fixing a position of a sheet-like substrate, and more particularly to a mechanism for fixing a position of a substrate as an object in an operation in vacuum.
2. Description of the Related Art
In recent years, a liquid crystal display device has become widely used as display means of a computer equipment and as a TV monitor. The liquid crystal display device has a liquid crystal display panel having liquid crystal sealed between a pair of glass substrates thereof, and shuts out light transmission through the glass substrates by changing alignment of liquid crystal molecules by voltage application to the liquid crystal, thereby plotting an image.
As a process mainly used for sealing the liquid crystal in the steps of manufacturing the liquid crystal display panel, there are methods called a vacuum injection method and a dropping method. The vacuum injection method is performed in the following manner. Specifically, a pair of glass substrates with a predetermined gap therebetween are disposed oppositely to each other, and a panel having a liquid crystal injection port is soaked in liquid crystal under vacuum after expelling air between the glass substrates. Thereafter, the pressure is returned to the atmospheric pressure, and thus the liquid crystal is injected into the panel by utilizing a pressure difference between the inside and outside of the panel and a capillary phenomenon. Meanwhile, the dropping method is performed as described below. Specifically, a sealing agent is applied in a frame shape to a periphery of one of a pair of glass substrates, liquid crystal is dropped onto a region surrounded by the sealing agent, and the other glass substrate is laminated onto the foregoing substrate. Thereafter, the sealing agent is hardened. The above-described dropping method is advantageous, compared with the vacuum injection method, in that time required for sealing the liquid crystal is significantly shortened. Therefore, in considering costs for manufacturing the liquid crystal display panel, the dropping method is an excellent manufacturing method.
In the above-described dropping method, upon lamination of the glass substrates, the glass substrates are desirably laminated in vacuum in order to avoid air bubbles remaining on a lamination plane. However, when the glass substrates are laminated in vacuum, there is a problem of how to hold the glass substrates in vacuum. In other words, in order to laminate the pair of glass substrates, it is necessary to fix and hold a position of at least one glass substrate and to perform positioning thereof with the other glass substrate. However, no appropriate means exists for holding the glass substrates.
Vacuum adsorption is one of the most commonly used methods of holding glass in the atmospheric pressure. However, in a vacuum state where a differential pressure is unobtainable, the vacuum adsorption cannot be used originally. In electrostatic adsorption using static electricity, adsorption in vacuum is possible. However, since electrical circuits are formed on the glass substrates of the liquid crystal panel, there is an accompanying risk of electrostatic discharge damage inflicted on these circuits due to the electrostatic adsorption.
According to a mechanical method of holding glass substrates, the glass substrates can be held in vacuum, and there never exists a problem such as the electrostatic discharge damage inflicted on the circuits. However, a mechanism itself is prone to become elaborate.
Since the gap between the pair of glass substrates constituting the liquid crystal display panel is as minute as 10 micrometers or less, the glass substrates are desirably fixed by a simpler mechanism in consideration of the followings: incapability of locking the substrates by hooking a plane for laminating the glass substrates with claws; and convenience in carrying the glass substrates in order to move to a step of hardening the sealing agent and the like after filling of the liquid crystal and lamination of the other glass substrate.
In addition, it is sufficient as long as a glass substrate, onto which the liquid crystal is dropped by the dropping method, is surely positioned on a support for setting this glass substrate. In this regard, it is not preferable that costs are increased because of provision of the mechanical holding means having the elaborate mechanism.